The world's largest flowers develop in two distinct ways.

The plants Rafflesia and Sapria are two groups within the same family (Rafflesia keithii pictured). Their gigantic flowers look similar, smell like rotting meat and form large chambers to lure carrion flies as pollinators.

But when researchers led by Charles Davis of Harvard University in Cambridge, Massachusetts, examined gene-expression patterns and physical structures of developing flowers, they found that the chambers of the two plant groups come from different tissues. This suggests that the groups evolved their most characteristic features independently.

The study might also help to explain how the flowers of some Rafflesia species can get as big as one metre across — the largest of all single blossoms — without collapsing. The flower chambers are derived from the petal whorl, which could provide structural reinforcement.

Credit: FRANS LANTING/CORBIS

Proc. Natl Acad. Sci. USA http://doi.org/pq9 (2013)